1. Field
The field hereof is mounting systems, in particular to methods and apparatus for mounting fasteners to hollow walls and ceilings.
2. Prior Art
Most walls and ceilings of residential and commercial structures have a hollow cavity construction, i.e., there is a hollow space behind the wall. The wall comprises a sheet of material, typically between 1 and 2.54 cm thick, affixed to a suitable frame which includes wood or metal framing members (studs or joists). These are typically spaced on 41 or 61 cm centers. Such sheet material is sold, e.g., under the trademark SHEETROCK by United States Gypsum Co., Chicago, and is known generically as drywall, wallboard, plasterboard, and gypsum board. Another less common wall and ceiling material with similar characteristics is plaster applied over a lath substrate. In the discussion below, the term “wall” includes ceilings.
A variety of fasteners are commercially available for attaching, hanging, or securing objects such as pictures, mirrors, shelving, cabinetry, towel racks, handrails and other objects to a wall at a location other than over the area where a framing member is located. Such fasteners can be divided into two main and general types: toggle and expansion.
Toggle fasteners generally comprise two components. The first component has spreading or tilting arms and is inserted with the arms folded into a drilled hole in the wall material. The second component, typically a screw or pin, is inserted into a hole in the first component and such insertion activates the first component by causing the arms to tilt or spread within the hollow space behind the wall, thereby locking the fastener in place on the wall.
Expansion fasteners are generally secured by causing their diameter to increase. Some comprise a first component which is hammered into a wall or inserted into a pre-drilled hole. A second component such as a pin or screw is forced into a central, cylindrical cavity within the fastener, increasing its diameter.
In addition to these two main types, a third type has tangs which springably expand to resist pull-out of the fastener.
The toggle and expansion fasteners suffer from significant disadvantages. These include the need for drilling the wall for the fastener, difficulty in tightening properly since over-torquing the fastener or the screw often results in much damage and hence failure of the wall, and/or an unsightly oversized hole when the fastener is removed from such an over-torqued condition. Some of these fastening systems are also non-removable or are difficult to remove without leaving a large, unsightly hole in the wall. In addition, expansion fasteners crush the friable drywall material, limiting the grip of the device in the wall. Fasteners which are hammered into the wall frequently cause “blow-out”, or local fracturing, of the wall material, again limiting the grip of the device in the wall and leaving an unsightly or relatively large hole at the fastener site.
The above copending '093 and '896 applications use a hinged anchor with an insertable activating member. These are superior in many respects to the above anchors but are not optimal because, while they significantly reduce blow-out of the wall, they still may tend to cause some damage and are not as robust as possible.